The invention relates to a process for generating a trajectory for a robotized system comprising a random number of mobile members participating in the accomplishment of the trajectory.
The trajectories of industrial robots are defined by successions of sections or portions joined by passage points where the system is in a given state. It very frequently occurs that in reality the trajectory results from the superimposing of several movements performed by different mobile members or by the same mobile member. An elementary example is that of a working tool such as a grinding wheel or milling cutter at the end of a robot arm. One of the movements is the displacement of the cutter or its centre on a curvilinear trajectory and another movement is its orientation. These movements are accomplished in an almost uncoupled manner by the robot arm and by the rotation of the wrist at the end of said arm.
Certain inadequacies of the conventional trajectory generation processes restrict the capacities of robotized systems. The method normally used for generating trajectories consists of defining the travel speed of the section for each movement. The movements then comprise an acceleration phase, a constant speed phase and a deceleration phase. With this method it is not possible to vary the speed of the movement in real time. It is also necessary to carry out preliminary calculations in order to define the travel times of the three phases, as well as the distances of portions of corresponding travels as a function of authorized acceleration and deceleration values. These calculations must be carried out once and for all and it is not possible to repeat them when the travel of the trajectory has been commenced, which means that it is impossible to modify the speed and that the movement is consequently fixed from the outset.
FIG. 1 summarizes this trajectory generating mode. It consists of a speed diagram as a function of time and the three successive phases are designated F1, F2 and F3, the slopes of F1 and F3 being imposed in the same way as V2 (maximum acceleration, deceleration and speed).
The invention relates to an improved process more particularly making it possible to automatically generate a trajectory in direct time, i.e., whose advance speed is not necessarily known beforehand and which can e.g., be controlled by a sensor preceding the working tool and which indicates the presence or size of a burr. For this purpose one of the movements is a main movement for which each section is traversed at a speed limited as a function of an acceleration and a deceleration of a maximum nature associated with the main movement and the other movements so as not to exceed a maximum speed at the end of the section presently being covered, the maximum speed being calculated in such a way as to be able to stop the mobile members, whose robotized system is composed at the end of the following section and in that the other movements are dependent on the main movement and are covered at variable speeds calculated as a function of the variable speed on the main movement so that all the movements simultaneously lead to the end of each section, i.e. terminate together. The maximum acceleration and deceleration, which can be chosen by the system designer, permit flexible movements and serve as a mechanical filter for excessively sudden variations of controls.
The speeds of the dependent movements can naturally be calculated in such a way that the proportion of the section covered by each of said dependent movements converges towards the section proportion covered at the same instant by the main movement, or a maximum acceleration or deceleration until the said proportions coincide.